The present invention relates to an extended-mobility tyre of the asymmetrical self-supporting sidewall type, having optimum comfort and behaviour characteristics.
For some years, tyre manufacturers have been devoting particularly great effort to developing original solutions to a problem dating back to the very first time use was made of wheels fitted with tyres of the inflated type, namely how to allow the vehicle to continue on its journey despite a considerable or total loss of pressure in one or more tyres. For decades, the spare wheel was considered to be the sole, universal solution. Then, more recently, the considerable advantages linked to the possible elimination thereof have become apparent. The concept of “extended mobility” is being developed. The associated techniques allow travel to continue with the same tyre, within certain limits, after a puncture or a drop in pressure. This allows the driver to travel to a repair point, for example, without having to stop, in frequently dangerous circumstances, to fit the spare wheel.
Two major types of extended-mobility technology are currently available on the automobile market. On the one hand, there are tyres of the self-supporting type (often known by their abbreviation ZP, standing for “zero pressure”). Self-supporting tyres are capable of bearing a load under reduced pressure, or indeed without pressure, thanks to sidewalls which are reinforced, most frequently by means of inserts of rubber material, provided in the sidewalls. This type of solution has the disadvantage of having relatively rigid sidewalls, which thus adversely affect the comfort and the endurance. Large masses of materials are necessary to impart to the sidewalls the rigidity required for the self-supporting function.
On the other hand, wheels are available which are equipped with supports capable of supporting the inside of the tread of a tyre in the event of sagging of the sidewalls following a drop in pressure. This solution is advantageously combined with a tyre comprising a bottom zone capable of minimising the risk of the tyre sliding out of the rim. This solution is advantageous since it makes it possible to keep substantially intact the characteristics of travel under normal conditions. On the other hand, it has the drawback of requiring an additional component, the support, for each of the wheels of the vehicle.